1. Field of the Invention
This invention relates to a method for controlling a winch of a mining machinery, such as a coal mining machine, an excavator or an ore carrier machine.
2. Description of the Prior Art
Generally speaking, the direction and speed of movement of a winch of a piece of mining machinery are controlled by the position of a controlling element of a fluid pump for supplying fluid (for example a liquid) into a working fluid pressure recirculating circuit. The position of the controlling element is controlled by an electromagnetic change-over valve by way of a fluid pressure cylinder connected to a fluid pressure control circuit. The electromagnetic change-over valve is operated by a push button switch connected to a control cable or a wireless push button switch.
For example, if a push button for operating a winch in the rightward moving mode, which is provided in a winch control device of a mining machinery is pressed, then an electromagnetic change-over valve for moving a winch to the right is excited, thereby operating the fluid pressure cylinder device in a direction to operate the winch to the right. Consequently, the controlling element of the fluid pump assumes a position to move the winch to the right, so that the winch starts moving to the right. If the push button is further pressed, the fluid pressure cylinder device continues to operate, thereby shifting the controlling element to a position in the high speed region, whereby the speed of the winch is increased. In short, the speed of the winch is controlled by the duration of which the push button is being pressed. Such a controlling method, however, has a drawback in that, because of the effect of the inertia of a winch device and the mining machinery itself and the slackening of the chain engaging the winch, an interval of time is introduced between the operation of a control system and the operation of the mining machinery itself. Furthermore, in a dark place in which feeble lights are lit, such as in the pit, an operator must continuously press the push button while watching by one's eyes the running conditions of the mining machinery, and it is difficult to control the winch so that the winch may be operated at a predetermined speed for the time during which the push button is being pressed.